Gas exhaust and cleaning system



July 23, 1968 M, DONNELLY 3,393,497

GAS EXHAUST AND CLEANING SYSTEM Filed May 5, 1965 5 Sheets-Sheet 1 //WW7'0Z RANK MDONNELLY,

July 23,1968 F. M. DONNELLY 3,393,497

GAS EXHAUST AND CLEANING SYSTEM ATWRNEW- July 23, 1968 F. M. DONNELLY GAS EXHAUST AND CLEANING SYSTEM 5 Sheets-Sheet 5 Filed May 5, 1965 mvamoa FRANK M.Do--ewr United States Patent 01 iice 3,393,497 Patented July 23, 1968 3,393,497 GAS EXHAUST AND CLEANING SYSTEM Frank M. Donnelly, 5773 Belmont Ave., Cincinnati, Ohio 45224 Filed May 5, 1965, Ser. No. 453,404 4 Claims. (Cl. 55-439) ABSTRACT OF THE DISCLOSURE A system for exhausting and cleaning gases containing vaporized and solid contaminants, comprising a collecting hood; a duct communicating with the hood; an exhaust fan positioned above the duct; a housing surrounding the fan and communicating with the duct; and at least one centrifugal extractor mounted in the hood through which the contaminated gases are drawn, the extractor comprising a planar front surface, a plurality of rectangular slots therein disposed in a circle, each slot being formed by lines of out along three sides of the rectangle defining a tab, the tab being bent backwardly along a line defining the fourth side of the rectangle at an acute angle with the front surface, a cylindrical drum of greater diameter than the circle of slots and concentric therewith secured to the rear of the planar surface, a rear closure plate parallel to the planar surface with a central circular discharge opening therein, an annular depending sleeve normal to the planar surface terminating in a free inner edge in spaced relation to the rear of the planar surface, each slot being non-radial whereby to force gases drawn through the slots to whirl in a confined vortex within the drum and to condense vaporized grease on the interior surface of the drum, the cleaned gases passing through the space between the sleeve and the rear of the planar surface and discharging through the central discharge opening into the duct.

This invention relates to a complete system for exhausting and cleaning gases, particularly heated contaminated air, and discharging the same to the outside atmosphere. More specifically, the invention provides a system for exhausting of cooking fumes, vaporized grease, combustion gases and heat given oif by commercial cooking equipment, comprising a collecting hood, a centrifugal grease extractor, an exhaust fan, and a section of ducting connecting the hood and the exhaust fan, which system is capable of exhausting hot gases containing volatile contaminants from a room to the outside atmosphere in an efiicient and fire-safe manner while removing and collecting substantially all the volatile contaminants before discharge of the gases to the outside atmosphere.

The idea of installing a canopy hood above a cooking surface is notoriously old, and the provision of exhaust fans and impingement type filters, or other types of grease extraction units, with ducting connecting the canopy hood and the exhaust fan, is also conventional in the art. However, despite the variety of such equipment now available, it is well known to restaurant operators and fire insurance underwriters that fire losses from cooking fires are increasing at an alarming rate. Despite the effort which have been made toward combining elements of conventional equipment to provide a complete and eifective system, the result has merely been an increasing complexity in currently available systems with consequent increases in cost without any appreciable improvement in results.

The intense competition among restaurants has, in effect, resulted in transformation of a commercial kitchen of moderate output into a highly efficient production unit utilizing the smallest possible amount of area for the greatest possible amount of continuous cooking. This has resulted in use of cooking equipment of greatly increased output, which has in turn multiplied the difficulties of disposing adequately of the increased heat generated as well as the increased amounts of combustion gases, heated air, grease vapors and other volatile contaminants. Discharge of grease vapors and other volatile contaminants into the outside atmosphere in increased amounts has given rise to the new problem of offensive odors in areas around restaurants. Although these problems have existed to a lesser degree in the past, the higher efiiciency of commercial kitchens has now outstripped the ability of conventional exhaust and filtering systems to cope with these problems.

The present invention is based on a novel approach to these problems which involves first a correlation of the requirements of the entire system with the total amount of heat being introduced by the operation, and next a recognition of the fact that two kinds of heat are involved, viz., radiant heat in the infra-red band, as well as convective heat resulting in an increased volume of heated air, combustion gases, etc. containing grease vapors and other contaminants of increased volatility. The approach taken by the instant invention disposes first of the radiant heat, and this in turn makes possible the exhausting and cleaning of heated gases containing volatile contaminants with much greater efliectiveness than any conventional systems. Surprisingly, it has been found that control of the radiant heat generated in the cooking operation makes it possible to clean and collect contaminants from the heated air and cooking gases more completely while exhausting much less air than is done in conventional equipment. This in turn avoids the problem of replacing the exhausted gases with large amounts of fresh outside air, which in cold weather naturally must be heated for the comfort of the personnel working in the kitchen.

The solution of the problem of removal of excess heat, both radiant and convective, along with removal of contaminated air, combustion gases, volatile grease vapors and odors, is achieved in part in the present invention by positioning the collecting face of the hood as near the cooking surface as is practicable, all-owing just sufiicient space for personnel to have access to the cooking surface. It is this feature which makes possible removal of objectionable contaminants, combustion gases, etc., while exhausting a lesser volume of air than is done in conventional systems. It should be understood that where conventional impingement-type grease filters are used, a much greater clearance above the cooking surface must be permitted in order to avoid absorption of the radiant heat by the filter media, which would impart this radiant heat directly to the exhaust gases being drawn through the filter media, thereby raising the temperature inside the hood and duct to a dangerously high level from the standpoint of fire hazard. The increase in temperature also decreases the density of the gases being exhausted, thereby resulting in reduced fan suction.

The conventional impingement-type filter also adversely affects the amount of gases which can be exhausted in another way in that its resistance to the flow of air or gases changes constantly as it gradually collects grease and lint. These two factors thus make it impossible for a system using conventional filters to exhaust a constant amount of air or gases from the cooking area. It is apparent that a decrease in the amount of air being exhausted results in a change in the thermal balance of the system so that the excess heat builds up to the point where hazard of fire exists.

The present invention overcomes these disadvantages by replacing the conventional impingement-type filter with a novel centrifugal grease extractor which possesses a face which reflects almost all the radiant heat back onto the cooking surface. In addition, its resistance to the flow of air and gases changes only very slightly as a result of the grease and lint which it collects. As a result this centrifugal grease extractor may be installed as close to the cooking surface as practicable.

A further contribution to the solution of these problems resides in the development of an exhaust fan which imparts the necessary energy of motion to the air and gases being exhausted in a different manner. Unlike conventional exhaust fans or blowers, the novel fan blade of the present invention generates a rotating whirl or conveying vortex in the air, the direction of rotation generated by the fan being in the same direction as the direction of rotation imparted to the exhaust gases as they are drawn through the centrifugal grease extractor. In this manner the normally wasted rotational energy imparted by the exhaust fan is put to efllcient use in the system of the present invention, since the rotational effect causes condensation of the grease vapors in the centrifugal extractor.

In avoiding air pollution the recent trend has been toward emphasis on water scrubbing of waste gases before discharge thereof to the outside atmosphere. In a preferred embodiment of the present invention water is caused to impinge against the rotating fan blades which break it up into a fine mist which scrubs objectionable odors and water-soluble contaminants from the exhaust gases before discharging them upwardly to the outside atmosphere. This water washing also condenses any grease vapors which may still be present in the exhaust gases, and has the further advantage of cooling the exhaust gases before discharge to the outside atmosphere.

It is thus a principal object of the present invention to provide a complete system comprising a hood positioned near the cooking surface, the hood having a plurality of centrifugal grease extractors which reflect radiant heat back to the cooking surface and which have relatively constant resistance to the flow of gases therethrough, and an exhaust fan which imparts rotational energy to the gases being exhausted.

It is a further object of the invention to provide a collecting hood of novel design and arrangement with respect to a cooking surface.

It is another important object of the invention to provide a centrifugal grease extractor which functions in a highly eflicient manner in close proximity to the cooking surface.

It is still another object of the invention to provide an exhaust fan having a novel fan blade combined in a section shaped to the conventional angle of a propeller blade with a section shaped to function as a backwardly inclined centrifugal blower wheel.

It is a further object of this invention to provide a system for washing exhaust gases with a fine mist of water before discharge of the gases to the outside atmosphere.

These and other objects of the invention, which will be pointed out hereinafter or which will be apparent to the skilled worker in the art upon reading this specification, are accomplished by that certain construction and arrangement of parts and in that procedure of which a certain exemplary embodiment will now be described. Reference is made to the accompanying drawings wherein:

FIG. 1 is a side elevation, partly in cross section, showing an embodiment of my novel exhaust system;

FIG. 2 is a cross-sectional view of the fan wheel of the present invention;

FIG. 3 is a top plan view of the fan wheel of the present invention;

FIG. 4 is a front perspective view of a part of the novel exhaust system showing the arrangement of the centrifugal grease extractors;

FIG. 5 is a cross-sectional view of the centrifugal grease extractor of the present invention;

FIG. 6 is a top plan view of the centrifugal grease extractor of FIG. 5;

FIG. 7 is a fragmentary cross-sectional view, taken on the line 7--7 of FIG. 6, showing a preferred slot and tab structure in the centrifugal grease extractor of FIG. 6;

FIG. 8 is a fragmentary plan view, partly in cross section, of the upper portion of an exhaust system showing the novel water wash system of the present invention; and

FIG. 9 is a top plan view of the water wash system 9-9 of FIG. 8.

Referring to FIGURE 1 of the drawing, a preferred system for installation in a commercial kitchen comprises a canopy hood indicated generally at 10, a plurality of centrifugal grease extractors secured in the hood (see FIG. 4) indicated generally at 11, a duct connected to the top of the hood indicated generally at 12, an exhaust fan assembly indicated generally at 13, and an exterior housing indicated generally at 14 surrounding the fan and its electric motor. A conventional gas or electric stove is indicated generally at 15.

The arrangement of the centrifugal grease extractors within the hood is shown in FIGS. 1 and 4. The front face 20 of each grease extractor is preferably of stainless steel which is highly reflective to radiant heat. The planar front surface 20, in the arrangement of FIG. 1, is inclined at an angle of more than 15 and less than 45 to the horizontal and the bottom of the grease extractor is posiioned approximately from 6 to 12 inches above the cooking surface. This has been found to produce excellent results in reflecting most of the radiant heat generated in the cooking operation back to the cooking surface.

As shown in FIGURE 5, each centrifugal grease extractor is provided with a flanged edge 20a preferably formed integrally with the front face 20 on all four sides of the unit. Arranged in a circle in the center of the front face 20 is a plurality of rectangular slots 21 angularly offset.

The slots may conveniently be formed by cutting three cuts or slits 22, 23 and 24 in the surface 20, and bending back each tab 25 along the bend line 26 (see FIG. 7). The tabs 25 direct the flow of gases which pass from the front surface 20 through the slots 21 due to the suction of the exhaust fan and imp-art to these gases a whirling motion. The angle of the tabs with the front surface is from to Each slot is angula-rly arranged in such a manner that a radius passing through the outer corner formed by the bend line 26 and the cut 24 forms an angle of from 5 to 20 with the bend line. Preferably this angle is 10, as illustrated in FIG. 6.

As the gases pass through the slots 21 and have a whirling motion imparted thereto they are initially confined within the cylindrical drum or enclosure 27 which has a diameter greater than that of a circle through the corners of the slots formed by cuts 23 and 24. The drum 27 has a back closure plate 28, with a central aperture, and connected thereto or integral therewith, there is provided an annular, inwardly extending sleeve 29 of substantially smaller diameter than that of a circle through the corners of the slots formed by cuts 23 and 24. The sleeve 29 extends inwardly toward the slots 21 but is spaced therefrom a distance suflicient initially to confine the flow of gases, then to permit the whirling gases to pass underneath the edges of the sleeve, escape through the central aperture and pass upwardly into the duct 12, without interfering with the flow of incoming gases through the slots 11. Sleeve 29 is preferably from /3 to of the depth of drum 27.

It will of course be understood that the vortex created within the cylindrical drum 27 causes vaporized grease, lint and other contaminants to be forced outwardly by centrifugal force and impinge against the cylindrical surface of the drum where they are condensed. The grease collected in this manner runs downwardly, passing beneath the juncture of drum 27 and the back of the surface 20, and is collected in the angle between the front face 20 and the flange 20a. Holes 30 are preferably provided at each corner of the extractor through which the collected grease will flow. By providing holes at all four corners it becomes unnecessary to identify the top and bottom of each extractor. Because of the proximity of the extractors to the cooking surface, the grease will of course at all times remain in a liquid condition.

The tops of the centrifugal extractors are 'detachably secured in place by a continuous bracket 31 which is constructed in the manner of a leaf spring so as to bear against the front surface of each extractor thereby creating a gas-tight seal to ensure against loss of suction. The rearwa'rdly facing edge of the flange 20a bears against an angularly inclined bracket 32 secured to the underside of the top of the canopy hood 10, as illustrated in FIG. 1.

The grease collected at the bottom of each extractor will flow, as stated previously, through holes at each lower corner of the extractor. The grease then drains into a bracket 33, shown in FIG. 1 which is shaped in such a way as to releasably hold the lower edges of the extractors, again with a gas-tight seal as is the case with the brackets 31. However, the brackets 33 are provided with at least one drain hole (not shown) through which the grease may flow by gravity into the collector cup 34. Running the entire length is a supplementary trough which catches any overflow from cup 34. The top of the cup 34 and trough 35 are visible at all times. Since a certain amount of lint and other contaminants which will not flow through the relatively small holes provided at the corners of the extractors will be collected within the cylindrical drum 27, handles 36 are provided on the surface 20 of each extractor so that it is readily possible to remove the centrifugal extractors from the hood. The drum 27 is then easily detached from the front surface 20 by manipulation of the simple twist lock means 37 and 38 for cleaning. The twist lock means comprise the four spring elements 37, shown in broken lines in FIG. 6, each of which is spot welded near its outer edge to the back of face 20. The free inner edges of elements 37 fit over and clamp flanged lower edges 38 of the cylinder 27. The flanged edge 38 is formed with four flat sections 38a, shown in broken lines in FIG. 6, each 90 apart. By twisting the drum 27 until the flat sections 38a are aligned with the springelements 37, and then deflecting the sides of the drum 27 slightly inwardly, the drum detaches from the elements .37.

After the gases being exhausted pass through the inclined slots 21 of the centrifugal extractors and thus have a whirling motion imparted thereto, the gases are drawn by the exhaust fan upwardly through the duct, indicated generally at 12, comprising a vertically disposed conduit 40 which-may be of square or circular cross-sectional configuration, and pass upwardly through a circular opening 41 at the top of the conduit which terminates adjacent the exhaust fan indicated generally at 13. A conventional curb of sheet metal indicated at 42 in FIG. 1, is provided for keeping rain, snow and outside air from entering the aperture in the roof through which the conduit 40 extends. Mounted on the curb 42 is a housing 43, of circular crosssection centered with respect to the opening 41. The housing 43 protects the opening 41 from outside elements and constitutes a means for directing the exhausted gases upwardly away from the roof. A supporting conduit 44, which may conveniently be a hollow tube-like element of square, rectangular or circular cross-sectional configuration open at its lower edge is secured across the top of the housing 43 by an annular depending band 44a to which it is welded.

The fan blade 45 (FIGS. 2 and 3) is of greater diameter than the diameter of the outlet 41 from the conduit 40. The blade is keyed to the shaft of motor 46, and the motor is surrounded by its bucket 47. Suflicient clearance between the bucket and the motor is provided to permit clean, cool air drawn through conduit 44 to pass over the motor for cooling purposes and then be mixed with exhaust gases and discharged. The electrical connection 48 to the motor can conveniently be I'Llln. through the conduit 44 to an outside source of electrical power 49.

The curb 42 may be of square configuration and has mounted around its outer periphery a collecting trough 50, which retains precipitation and also collects grease which has been thrown outwardly by the action of the fan blade 45 and has condensed on the inner wall of housing 43 whence it flows by gravity through a plurality of perforations 51 near the bottom of the housing 43 across the curb 42 into the trough 50. A grease skimmer 52 is provided which cooperates with a downwardly depending flange 53 of the curb 42 to entrap the collected grease therebetween, permitting excess water to overflow over the outer edge of trough 50 without permitting grease to overflow. This arrangement prevents any unsightly deposit of grease from being discharged onto the roof of the building, thereby reducing fire hazard.

The upper portion of the conduit 40, the curb 42 and the outer housing 43 together with the collecting trough 50 and associated grease skimmer are supported in conventional manner by studs 54 which in turn are secured to the roof 55. It will of course be understood that in the case of a slanting roof, the studs will be configured in such a :manner as to support the curb 42 in a substantially horizontal plane, although the trough 50 will function satisfactorily even if tilted to an angle of 5 to 10 away from the horizontal.

The novel fan wheel 45 of the present invention is illustrated in FIGURES 2 and 3. It 'will be seen that the fan wheel comprises a web 56 along the upper surface of the wheel which is of thicker cross section than the remaining parts of the structure in order to impart sufficient rigidity and strength to the wheel. A plurality of fan blades, which may vary between four and eight, (there being four blades illustrated in the exemplary embodiment of FIGS. 2 and 3) depend outwardly and downwardly from the web 56. Each blade comprises a section 57 shaped in the form of a propeller blade and a section 58 which functions in the manner of a backwardly inclined centrifugal blower blade when rotated in the direction indicated in FIG. 3. The sections 57 and 58 are of substantially equal surface area, and optimum results have been obtained with the section 57 disposed downwardly at an angle of about 30 from the horizontal. The hub 59 of the fan Wheel has a keyed aperture *60 therethrough of a diameter which will fit over the shaft of the electric motor 46.

The fan wheel 45 may conveniently be formed of cast aluminum which is machined to balance the wheel and to provide relatively accurate dimensions for the sections 57 and 58 and the aperture 60.

When operating with a one-half horse power motor, excellent results have been obtained using a fan wheel 14 inches in diameter with the outlet 41 from the conduit 40 ten inches in diameter. The diameter of the fan Wheel may vary from 12 inches to 18 inches when using a one-half or a one horse power motor with outlet openings 41 from the duct varying correspondingly between 10 inches and 12 inches.

The discharge velocity of the fan blade is by design relatively low, but its capacity is suflicient to exhaust from 200 to 450 cubic feet per minute through each of the centrifugal grease extractor units installed in the canopy hood. In an installation having eight centrifugal grease extractor units, a fan blade of 16 inch diameter exhausted about 300 cubic feet per minute for each extractor, or a total of 2400 cubic feet per minute through outlet 41 which was ten inches in diameter. Excellent results were obtained when operating under these conditions.

In order to vary the suction and consequent capacity of the exhaust fan, angular slots 61 are provided in the annular band 62 which supports the motor bucket 47 within the outer housing 43 as shown in FIGURES 1 and 8. By loosening connecting bolts 63 which project through the angular slots 61, the annular band may be rotated with respect to the outer housing 43 so that the entire assembly including fan wheel 45, motor 46 and bucket 47 will be drawn upwardly away from the orifice 41 (thereby reducing suction) or lowered closer to orifice 26 (thereby increasing suction), thus providing a variable suction fan without change in rotational speed of the fan blades. The bolts are then tightened in the desired position in order to maintain the desired setting.

In a test installation of the type illustrated in FIGURE 1, wherein the centrifugal grease extractors were positioned at an angle of about 35 eight inches above the cooking surface, it was found that the temperature of the exhaust gases in the duct was from 90 to 140 F. When it is realized that the temperature of the exhaust gases in the ducts of conventional exhaust systems vary from 250 to 400 F., even though the impingement-type filter elements are required by code to be positioned at least from 2 /2 to 4 /2 feet above the cooking surface, the marked improvement in the operation of the present system will be apparent. The hazard of fire is reduced to a minimum as a I'Ctilllt of the low temperature prevailing throughout the centrifugal grease extractors and the duct, even though gases are exhausted at the relatively low rate of about 200 to 450 cubic feet per minute for each grease extractor unit. Removal of grease vapors from the exhaust gases by the centrifugal grease extractor units was found to be more eflicient than conventional impingement filters. Grease vapors remaining in the exhaust gases were substantially removed by the action of the fan wheel which caused the remaining grease vapors to condense on the inner wall of the housing from which it was collected in the grease skimmer.

When the water wash system of the embodiment shown in FIGS. 8 and 9 is used, practically complete removal not only of grease vapors, but also of fumes, odors and other volatile contaminants is assured. Moreover, the mist of water lowers the temperature of the exhaust gases approximately to the ambient temperature of the outside atmosphere.

In the embodiment of FIGS. 8 and 9 corresponding parts to those of FIG. 1 are indicated by like characters of reference. It will be noted that a complementary curb member 65 is provided which mates with and is positioned in closely spaced relationship with the curb 42. At the outer edges of member 65 a downwardly depending flange 66 is provided which is also in closely spaced relation to the flange 53 of the curb 42. As shown in FIG. 8 the flange 66 is secured to and forms the inside wall of the trough 50, although it will of course be understood that flange 66 may be a separate member having no contact with the trough but will in that event project down into it beneath the normal water level in the trough. Flange 53 also projects downwardly into trough 50 beneath the normal water level therein.

The arrangement of curb 42 and its flange 53 and the complementary member 65 and its flange 66 is such that water in the trough 50 is drawn vertically upwardly apparently at least partially by capillary action, in the space between flanges 53 and 66, and then horizontally in the space between curb 42 and member 65, toward the opening 41, where it comes undr the influence of the suction created by the fan wheel 45. The suction of the fan wheel draws drops of water out of the upwardly flaring edges of curb 42 and member 65 at the opening 41, and these drops are broken up into a fine mist upon contacting the blades of the fan wheel. The mist is thrown outwardly (with a slight upward vector) against the inside walls of housing 43. In so doing the water mist thoroughly scrubs the gases being exhausted upwardly through housing 43, extracts therefrom water-soluble odors and contaminants, and also condenses grease vapors remaining in the exhaust gases. The moisture and condensed grease then run down the inner wall of housing 43 and are collected on the upper surface of curb 42. The water and grease flow through openings 51 in housing 43 out over curb 42 and into the trough 50 where the Water is reused in the same manner while the grease is collected by the skimmer 52.

In the event that natural precipitation is not suflicient to keep the water level in trough 50 above the downwardly projecting edge of flange 53, a float valve 67 is provided in one corner of the trough 50 which is connected to a water line 68 carrying water under pressure. When the water level drops below the edge of flange 53, the float valve is actuated to admit water into the trough through line 68 until the predetermined level has been reached, at which time the float valve 67 shuts off the water supply.

The trough, curb, and complementary member need not be positioned exactly horizontally in order to have the water wash system function effectively. It has been found that good results are obtained even when the assembly is tilted to the extent that only one side of the trough at which the float valve is located has water therein. This is of course advantageous when the installation is to be made in a building having a sloping roof.

It will be understood that numerous modifications may be made without departing from the spirit of the invention, and I therefore do not intend to limit myself otherwise than as set forth in the claims which follow.

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. In apparatus for exhausting, cleaning, and discharging to the outside atmosphere heated gases containing vaporized grease, solid contaminants and the like produced by cooking equipment, the combination of a collecting hood positioned closely above a cooking surface; a duct communicating with said hood; an exhaust fan positioned above said duct having a fan wheel which generates a suction; a housing surrounding said exhaust fan and communicating with said duct; said hood, duct and housing defining an exhaust passage through which said gases are sucked by said fan Wheel; and at least one centrifugal extractor mounted in said hood through which said gases are drawn, said extractor comprising a substantially planar front surface inclined at an angle of more than 15 and less than 45 to said cooking surface with the bottom edge of said extractor not more than 1 foot above said cooking surface, a plurality of rectangular slots in said front surface arranged in a circle, each slot being formed by lines of cut on three sides of the rectangle defining a tab, said tab being bent rearwardly along a bend line defining the fourth side of said rectangle at an angle of from 35 to 55 with said front surface, a cylindrical drum of greater diameter than said circle of slots and concentric therewith secured to the rear of said planar surface, said drum having a rear closure plate substantially parallel to said planar suface with a circular central discharge opening therein, an annular inwardly depending sleeve substantially normal to said planar surface secured to said rear closure plate, said sleeve being concentric with and of smaller diameter than a circle through the outer corners of said slots, said sleeve terminating in a free inner edge in spaced relation to the rear of said planar surface, each of said slots being angularly inclined in such manner that a radius of said circle passing through the corner formed by said bend line and a line of cut forms an angle of from 5 to 20 to said bend line, whereby air and heated gases drawn through said slots are caused to whirl in a confined vortex within said drum to force vaporized grease and solid contaminants outwardly against the interior surface of said drum, on which surface the vaporized grease is condensed to form a liquid film which effects adhesion of said solid contaminants, under the influence of centrifugal force, the cleaned gases being then displaced inwardly toward the axis of said drum, passing through the space between said annular sleeve and the rear of said planar surface and discharging through said central discharge opening into said duct.

2. The apparatus claimed in claim 1, including means 9 for varying the suction of said exhaust fan, without change in the rotational speed of said fan wheel.

3. The apparatus claimed in claim 1, wherein a plurality of centrifugal extractors is disposed in substantially horizontal alignment within said hood, the planar front surface of each extractor being of stainless steel, and including substantially horizontal brackets in said hood engaging the upper edges of said extractors, at least one of said brackets being constructed in the form of a continuous leaf spring bearing against said planar front surfaces to form an air tight seal therewith.

4. A centrifugal extractor for use in apparatus for exhausting, cleaning and discharging heated gases containing vaporized and solid contaminants, comprising a substantially planar front surface of stainless steel, a plurality of rectangular slots in said front surface arranged in a circle, each of said slots being formed by lines of cut in said front surface on three sides of the rectangle defining a tab and said tab being bent away from said front surface along a bend line defining the fourth side of said rectangle at an angle of 35 to 55 with said front surface, a cylindrical drum of greater diameter than said circle of slots and concentric therewith secured to the rear of said front surface, said drum having a rear closure plate with a concentric circular opening therein, an annular, concentric inwardly depending sleeve secured to said closure plate terminating in a free inner edge in spaced relation to the rear of said front surface and substantially normal thereto, said sleeve being of lesser diameter than a circle through the outer corners of said slots, each of said slots being angularly inclined with a radius of said circle passing through the corner formed by said bend line and a line of cut forming an angle of from 5 to 20 to said bend line, the arrangement being such that air and heated gases drawn by suction through said slots past said planar surface are caused by said tabs to whirl in a confined vortex within said drum thereby forcing vaporized and solid contaminants against the interior surfaces of said drum where said vaporized contaminants are condensed forming a film to effect adhesion of said solid contaminants, the so cleaned gases then being displaced inwardly and passing through the space between said annular sleeve and the rear of said planar surface and discharging through said circular opening, and means for locking said cylindrical drum to the rear of said front surface, said locking means comprising a plurality of spring elements secured to the rear of said front surface each having an inwardly extending tangential free edge, a flanged edge on said drum, a plurality of interruptions in said flanged edge adapted to be aligned with said spring elements, said free edges of said spring elements overlying and clamping said flange when in the locked position and permitting removal of said drum when it is rotated so as to align said interruptions with said spring elements.

References Cited UNITED STATES PATENTS 18,293 9/1857 Naughten 55-178 1,059,802 4/1913 Williams 230-134.45 1,511,541 10/1924 Thompson 230-134.45 1,827,225 10/1933 Ferreby 230-134.45 1,939,248 12/1933 Bennett 55-452 2,162,152 6/1939 Wulle 55-482 2,613,786 10/1952 Ernrick 230-134.45 2,804,171 8/1957 Yellott et a1. 55-348 2,937,712 5/1960 Woods 261-30 3,021,777 2/1962 Smith 98-115 3,324,629 6/1967 Graswich et a1 55 1,981,549 11/1934 Hawley 55-450 2,363,437 11/1944 Peterson 230-134 2,889,836 6/1959 Maley 55-337 FOREIGN PATENTS 486,585 6/1938 Great Britain.

HARRY B. THORNTON, Primary Examiner.

B. NOZICK, Assistant Examiner. 

